114 NATURAL HISTORY OF WASPS. 
which a flymg machine should be constructed. From 
this, aud from a Lecture by Dr. Pettigrew,* I have 
endeavoured, without entermg too deeply into the 
question, to gather as much as may be read with 
interest im connection with the flight of wasps. 
Though the flight of insects is only discussed inci- 
dentally and by way of illustration to that of Birds 
by the Duke of Argyll,t yet I must add his thought- 
ful work to the list of authorities on this subject. 
The first thing to be attended to in the construc- 
tion of a flying-machine is of course how it shall 
support itself in the air; for such a machine, to have 
an independent motion, must be heavier than the 
surrounding medium. This principle is not satisfied 
in the construction of balloons; these cannot be re- 
garded in any proper sense of the word as flymg 
machines; they simply float about in the air, while 
the supporting power of the gas lasts, whichever 
way the wind may drive them. And our power of 
guiding these unwieldy monsters is limited pretty 
much to raising and lowering them, and to takmng 
advantage of the different direction of the currents of 
air to be found, if so it should happen, at different 
heights. A parachute perhaps is a step nearer to a 
real flying machine, though it can only be compared 
to a flying squirrel, or to a beetle deprived of its 
wings dropping gently down, by the aid of its elytra, 
to the ground. A child soon learns to turn the sup- 
porting power of the air to advantage when he plays 
* On the various Modes of Flight in relation to Aéronautics. 
‘ Journal of the Royal Institution of Great Britain,’ March 22, 1867. 
+ ‘The Reign of Law,’ small 8vo, London, 1867, particularly 
Chapter III, on the Machinery of Flight in Birds. 
